Polymeric articles with three-dimensional (3D) structures are usually manufactured by different molding methods. However, due to the limitation of the mold development and de-molding process, only 3D objects with simple structures can be obtained. Moreover, the molding process has the disadvantage of long development cycle of the molds, large investment and low efficiency.
3D printing, also known as additive manufacturing, is a process used to synthesize a 3D object in which successive layers of material are accumulated layer by layer under computer control to create the object. 3D printing is a directly prototyping technology which can create almost any shape or geometry from digital 3D data without any specific molds. It has been widely used in molding, industrial or art design, and direct fabrication of some products. However, the time for printing a single object is relatively long because of the layer by layer printing manner for all kinds of 3D printing technology such as Fused Deposition Modeling (FDM), Stereo Lithography Apparatus (SLA), Digital Light Processing (DLP), Selective Laser Sintering (SLS) and so on. The printing time significantly increases if a higher resolution is acquired, for the object should be cut into much thinner layers in this case. Although the technology of CLIP (Continuous Liquid Interface Production) from Carbon 3D company has relatively improved the printing speed, the absolute printing speed is still low.
Transforming a heterogeneous 2D sheet into a 3D structure under a certain condition is a unique manufacturing technology. The basic principle is introducing a chemical structure distribution inside a polymer matrix to yield a heterogeneous material. The chemical structure distribution can be a crosslinking density variety across the network, which can induce a certain internal stress. The internal stress can be released under certain conditions, leading the mechanical unsteady heterogeneous sheet transfer into a specific 3D structure. The design and fabrication of 2D sheet are easy and fast, as well as that of the transforming process. So the above-mentioned method can be a potential technique for fast constructing 3D structures. So far, the heterogeneous 2D sheet is mainly constructed through introducing a locally secondary network into a primary homogeneous network. The distribution of the secondary network, which determines the final 3D structure, is mainly introduced by using a photo mask. In this case, only simple 3D structure can be created because of the physical limitation of the photo mask.